Biological Rhythms: Circadian

Question 1

Biological Rhythms:

Answer 1

Distinct patterns of changes in body activity that conform to cyclical time periods.

Question 2

Circadian Rhythm:

Answer 2

A type of biological rhythm, subject to a 24 hour cycle, which regulates a number of body processes such as the sleep/wake cycle and changes in core body temperature.

Question 3

How are biological rhythms governed?

Answer 3

1. Body’s internal biological ‘clocks’ called endogenous pacemakers.
2. External changes in the environment known as exogenous zeitgebers.

Question 4

What does the fact that we feel drowsy at night and alert during the day demonstrate ?

Answer 4

Demonstrates that light is an important exogenous zeitgeber.

Question 5

Siffre’s: Aims

Answer 5

1. Find out what it would be like for astronauts in space, where there no exogenous zeitgebers to affect our biological rhythms.
2. Find out what his natural sleep-wake cycle would be without any exogenous zeitgebers.

Question 6

Siffre: Procedure

Answer 6

1. 14 February 1972 went into the Midnight Cave and stayed there for 6 months.
2. Took a supply of frozen food and 780 gallons of water.
3. When he woke up and thought it was daytime, he phoned the research team and they switched the lights on. Same for night.
4. Took memory, physical tests and blood pressure daily.

Question 7

Siffre: Findings

Answer 7

1. Became depressed at his lack of freedom and was so lonely that he would trap mice, accidentally killing them in the process.
2. Contemplates suicide and his eye sight and short term memory worsened.
3. For the first 37 days, sleep cycle 26 hours.
4. 37 onwards sleep for several hours, stay awake for a few hours for a month.
5. By day 150 to the end he stayed on a 26 hour cycle.

Question 8

Miles et al (1977):

Answer 8

1. Blind people show the same pattern as sighted people.
2. Suggests that external factors are important, but there are also endogenous pacemakers.
3. The principle mechanism that governs these rhythms appears to be suprachiasmatic nuclei (SCN).

Question 9

Jurgen Aschoff and Rutger Wever (1976):

Answer 9

1. A group of participants spent 4 weeks in a WWII bunker, without natural light.
2. All but one participant (whose sleep/wake cycle extended to 29 hours) displayed a circadian rhythm between 24-25 hrs.
3. Both Siffre and this suggest that the ‘natural SWC may be slightly longer than 24 hrs but is entrained by exogenous zeitgebers. Like no. daylight hours and meal times.

Question 10

Simon Folkard et al. (1985):

Answer 10

1. Studied a group of 12 that agreed to live in a dark cave for 3 weeks.
2. They slept when the clock read 11:45pm and woke up when it said 7:45am.
3. Over the course of the study they (unbeknown to the pps) sped up the clock.
4. An apparent 24hr day lasted only 22hrs. Only 1 pp adjusted comfortably to the change.
5. A strong free-running circadian rhythm that cannot be easily overriden by changes in the environment.

Question 11

E: Application to shift work

Answer 11

1. Has given researchers a better understanding of the adverse consequences that can occur as a result of disrupting the CR (desynchronisation)
2. Night workers engaged in shift work experienced a period of reduced concentration at 6 in the morning (circadian trough), making accidents more likely (Boivin et al. 1996)
3. Research has also suggested a relationship between shift work and poor health.
4. (Knutsson 2003) shift workers are x3 more likely to develop heart disease.
5. May be because of the stress of adjusting to different sleep/wake patterns.
6. May have economic implications in terms of how to manage worker productivity.

Question 12

E: Practical Application to Drug Treatments

Answer 12

1. CRs co-ordinate basic bodily processes like heart rate, digestion and hormone levels.
2. This in turn has an impact on pharamacokinetics, the action of drugs on the body and how well they are absorbed and distributed.
3. Research into CRs shows that there are peak times during the day or night when drugs are likely to be at their most effective.
4. This has led to the development of guidelines to do with the timing of drug dosing for a whole range of medications including anticancer, cardiovascular, respiratory, anti-ulcer and anti-epileptic drugs (Baraldo 2008).

Question 13

E: Use of Case Studies

Answer 13

1. Tended to involve small groups of participants (Aschoff and Wever) or studies of single individuals (Siffre).
2. May not be representative of the wider population and this limits the extent to which meaningful generalisations can be made.
3. In Siffre’s most recent cave experience in 1999, he observed at 60, his internal clock ticked much more slowly than when he was a young man.
4. Even when the same person is involved, there are factors that vary which may prevent general conclusions being drawn.

Question 14

E: Poor Control in Studies

Answer 14

1. Although participants in the studies were deprived of natural light, they still had access to artificial light.
2. Siffre turned on a lamp every time he woke up and turned it off when he fell asleep.
3. It was assumed by him and others that artificial light would have no effect on the free-running biological rhythm.
4. Charles Czeisler et al. (1999) were able to adjust participants’ circadian rhythms from 22 to 28 hours using dim lighting. Using light may be analogous to participants taking a drug that resets their biological clock.

Question 15

E: Individual Differences

Answer 15

1. Individual cycles can vary from 13 to 65 hours, complicates the generalisation of findings from studies. (Czeisler et al .1999)
2. In addition, a study by Jeanne Duffy et al. (2001) revealed that some people display a natural preference for going to bed early and rising early (‘larks’) whereas some are the opposite (owl)